1. Field of the Invention
The present invention relates to power supply systems, and more specifically to a plurality of power supply modules connected in parallel to a load and having associated ORing elements operable to selectively couple and decouple the outputs of each module to the load. The ORing elements may be controlled to isolate a faulty power supply module from the load under various conditions of system failure or sub-optimal performance.
2. Description of the Prior Art
There are a variety of conventional electrical power supply modules which include power converters that convert electrical power from one form into another. An example of this involves the conversion of AC power into DC voltage. The efficient performance of such power supply modules depends upon many factors, including the operation of the primary AC power source, the forward converter circuit, the auxiliary secondary voltage source, and the element used to couple the converted power to the load. A failure arising in any of these elements can lead to problems affecting the performance of the module and the power supply system of which the module is a part.
In conventional power supply systems, it is known to use a Schottky diode placed in series with the output of a power converter to isolate the output node of a faulty power supply from the load. This element is conventionally termed an "ORing" diode, (e.g., combining). The Schottky diode functions primarily as a switch, decoupling the output of a power supply (e.g., power converter) module from the load when a power failure occurs. One purpose for this arrangement is to prevent an interruption of the power to the load in the event of a failure or improper operation of a power supply module. For example, a DC bus typically connects all power supplies to each other and to the load, with the bus being highly susceptible to having DC bus voltage pulled down by such a failure. In most cases, the load is critically dependent on having a continuous source of well regulated DC voltage from the DC bus for its correct operation.
Although the technique of using a Schottky diode provides good system reliability, this approach has the disadvantage that the diode will dissipate an appreciable amount of power. This in turn reduces the efficiency of the power supply system. Accordingly, it would be desirable to reduce the amount of power dissipation by replacing the diode with an ORing element that has a lower voltage drop. Such an ORing element would need to be capable of simulating the characteristics and operation of a diode, while providing acceptable system reliability.
As the present inventors have realized, in order to improve system reliability, it is desirable that the ORing element be capable of isolating the power supply module from the load not only when the AC power supply fails, but also when a short circuit occurs in the power converter. It is also desirable that the ORing element be controllable to decouple the power supply module from the load when the power supply module delivers excessive voltage to the load.
Furthermore, it is also desirable for the ORing element to prevent spikes, dips or other anomalies in the voltage appearing at the load when the ORing element couples and decouples the power supply module with and from the load.
Still furthermore, it is desirable to have selective control of the ORing element to assist in detecting the failure of a power supply module, and to take into consideration situations contributing to false indications of failure of the power supply. The ORing element should also be controllable to prevent voltage dips or variations on the DC bus caused if a capacitor or rectifier circuit which is part of the power supply module should incur a short circuit. Moreover, the element should be reliable during step load changes, hot swapping and system power up conditions.
In a redundant power supply system, the power supply modules are commonly connected in parallel to provide increased power to a single load. Thus, it would be desirable to incorporate the features mentioned above in a parallel redundant power system to protect components connected at the load when failure conditions arise and are not properly responded to by a particular ORing element. These failure conditions can affect the voltage delivered to the load by the remaining functioning power supply modules. Therefore, it would be desirable to have a method of controlling the ORing element(s) to cause them to react to a variety of power failure conditions in a parallel mode or in a stand-alone mode, both of which will be defined in detail subsequently.
As the present inventors have realized, situations that should be addressed by such controllable ORing elements include undervoltage protection ("UVP") and overvoltage protection ("OVP"). These are defined to be the limits within which the ORing element and components of the system will properly operate and will be described in more detail subsequently. Such operation will ensure that only a faulty power supply module or modules would be isolated from the load, where for example, a number of power supply modules are operating to provide voltage to a DC bus connected to the load.